This invention relates to the vaporization of liquids and to an apparatus for feeding a special gas, produced by the vaporization of a liquid, to a semiconductor manufacturing line or the like.
There are two principal kinds of conventional liquid vaporizing and feeding apparatus. In one such apparatus, a vaporizer, in which a vaporizing portion is built into a control valve, is combined with a flow meter for liquid or a flow meter for gas. In another such apparatus, a vaporization container is combined with a sensor for responding to the amount of liquid, a liquid temperature controller, a gas flow controller, conduits for the inflow and outflow of liquid, and an open-and-shut valve. These components are all located in a temperature-controlled container.
A vaporizing and feeding apparatus which vaporizes liquid in a liquid container is not subject to the problems of pyrolysis of the liquid and foaming in the container, since the apparatus is heated from the outside of the container, and the liquid is present in the container in the form of a pool. However, since the container wall, which is typically made of stainless steel or the like, is situated between the heater and the liquid, the apparatus has a low vaporization efficiency.
A vaporizer in which a vaporizing portion is built into a control valve is disclosed in Japanese Unexamined Patent Publication No. 156055/2001. This apparatus improves vaporization efficiency by providing a uniquely shaped mixing portion for liquid and carrier gas.
Although not used for semiconductor manufacture, an apparatus which vaporizes and feeds liquid raw materials for glass is disclosed in Japanese Unexamined Patent Publication No. 256036/1994. This liquid material vaporizing and feeding apparatus improves vaporization efficiency by providing convexities and concavities inside a vaporization container, thereby increasing the heating area.
The vaporizer of Japanese Unexamined Patent Publication No. 156055/2001, in which the control valve has a vaporization function, is small in size. However, particles and contamination are generated in the vaporizer, since liquid materials are readily decomposed by partial heating. This vaporizer has other problems, in that its ability to vaporize liquid deteriorates, and proper control is not achieved because of foaming taking place in the liquid within the container.
Although the vaporization apparatus of Japanese Unexamined Patent Publication No. 256036/1994, has high vaporization stability, the apparatus itself is large, and the amount of liquid in its tank is also large. Therefore, since the space required for its installation is large, the apparatus cannot easily be built into semiconductor manufacturing equipment. Moreover, since the amount of liquid utilized in the apparatus is large, and liquid exchange is required for maintenance, the cost of the expensive liquid materials required for maintenance is high, and a large amount of time is required for removal of liquid when the maintenance is carried out.
A liquid vaporizing and feeding apparatus in accordance with the invention, which addresses the aforementioned problems, comprises a vaporization container and a vaporization plate within the container, preferably located at the bottom of the container. The plate is inclined relative to the horizontal. Means are provided for heating the vaporization plate, and means are provided for feeding liquid onto the vaporization plate adjacent the upper end thereof.
A liquid level detection means is responsive to the level of liquid collected on the vaporization plate, and means responsive to the liquid level detection means controls the feed of liquid onto the vaporization plate by the feeding means.
The liquid level detection means includes a capillary tube, a lower end of which is arranged to be contacted by the surface of the liquid collected on the vaporization plate when the volume of liquid reaches a desired volume. The capillary tube is associated with a thermal sensor, and provides liquid level detection with a high degree of sensitivity.
The flow of vaporized gas produced by the vaporizing and feeding apparatus is controlled by a mass flow controller, which, in a preferred embodiment, is a pressure type mass flow controller.
In the invention, since the vaporization plate is held at a certain temperature which is in accordance with the vaporizing condition of liquid materials, the influence of pyrolysis of liquid materials may be reduced and relatively large amount of vaporization flow may be obtained with a small vaporization area.
Even if the amount of liquid introduced into the vaporization container is not large, adequate vaporization flow may be obtained by inclining the vaporization plate relative to the horizontal. Therefore, the apparatus can be miniaturized, and the time and cost of maintenance, which requires liquid exchange, can be decreased.